Stepping motors are well known for converting electrical pulses into rotating mechanical movement. The first stepping motor was invented in 1936 by Mr Lavet for the clock and watch making industry; and since then these motors are found driving the movement in most quartz watches with hands. This type of motor is also commonly found in all devices where one wishes to control speed or position.
“Lavet” motors have permanent magnets that can generate stable positions between electrical pulses. The permanent torque thus exerted on the rotor, i.e. the rotating part of the motor, is supposed to prevent any inadvertent movement thereof, even when the watch undergoes shocks. The purpose of the permanent torque, which is generally selected to be considerably greater than the motor torque, is also to prevent any incrementation of more than one step simultaneously. These positioning torques do not, however, completely lock or incrementally index the meshed wheels; click systems have consequently been proposed for cooperating with these motors to improve the hold and lock functions, as for example in U.S. Pat. No. 4,647,218. In this Patent, a Lavet motor drives a wheel in rotation through 180 degrees with each electrical pulse, i.e. every minute; the wheel is fitted at two diametrically opposite ends with spigots, which engage in successive radial slots in the minute wheel. Thus, between each pulse, the two spigots are engaged in two successive radial slots of the minute wheel and prevent any possible movement thereof.
Now, other types of stepping motor are available, for example the micromechanical electromotor disclosed in EP Patent No. 1921520 by the Applicant, which includes a linear actuator fitted with an active click for driving the wheel in rotation, and a passive click for preventing the rotor from rotating in the opposite direction when the actuator returns during its oscillations. For this motor, the same locking and unitary incrementation functions would also be desirable. However, it is clear that the click mechanism described above, specific to a Lavet motor, is not suitable.